import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int m;
		double km;
		int tmp1, tmp2;
		String output;
		
		while(sc.hasNext()) {
			m = sc.nextInt();
			km = m * 1.6d;
			
			output = Double.toString(km) + "0";
			
			tmp1 = Integer.parseInt(output.substring(output.indexOf('.') + 1, output.indexOf('.') + 2));
			tmp2 = Integer.parseInt(output.substring(output.indexOf('.') + 2, output.indexOf('.') + 3));
			
			output = output.substring(0, output.indexOf('.'));
			
			if(tmp2 >= 5d) {
				tmp1 ++;
			}

			output += ("." + Integer.toString(tmp1));
			
			System.out.println(output);
		}
	}
}